The present invention relates to radiation therapy machines for treatment of tumors and the like and in particular to an intensity modulated radiation (IMRT) therapy machine for specialized treatment of portions of the body.
In external beam radiation therapy, high-energy radiation is directed through a patient to the site of a tumor. Multiple beams intersecting at site of a tumor may be used to reduce the dose to the skin and other intervening tissue. The individual beams may be collimated to the outline of the tumor to further reduce exposure of healthy tissue surrounding the tumor.
In intensity modulated radiation therapy (IMRT) the intensity of individual rays within the beams is adjusted to produce more complex dose patterns resulting not simply from the juxtaposed outlines of the beams but from the additive overlay of the rays of different intensities within the beams.
In Tomotherapy, an extremely large number of beams are directed through 360 degrees toward the patient from the rotation plane and the patient is treated in a series of slices. Individually modulated rays within each beam provide precise irradiation of irregular tumor shapes at greater speed and accuracy than conventional IMRT designs.
Tomotherapy machines and techniques are described in U.S. patents: U.S. Pat. No. 6,636,622 “Method and apparatus for calibration of radiation therapy equipment and verification of radiation treatment; U.S. Pat. No. 6,618,467 “Megavoltage computed tomography during radiotherapy”; U.S. Pat. No. 6,560,311 “Method for preparing a radiation therapy plan”; U.S. Pat. No. 6,438,202 “Method using post-patient radiation monitor to verify entrance radiation and dose in a radiation therapy machine”; U.S. Pat. No. 6,385,286 “Delivery modification system for radiation therapy”; U.S. Pat. No. 6,345,114 “Method and apparatus for calibration of radiation therapy equipment and verification of radiation treatment”; U.S. Pat. No. 5,724,400 Radiation therapy system with constrained rotational freedom”; U.S. Pat. No. 5,673,300 “Method of registering a radiation treatment plan to a patient”; U.S. Pat. No. 5,661,773 “Interface for radiation therapy machine”; U.S. Pat. No. 5,625,663 “Dynamic beam flattening apparatus for radiation therapy”; U.S. Pat. No. 5,548,627 “Radiation therapy system with constrained rotational freedom”; U.S. Pat. No. 5,442,675 “Dynamic collimator for radiation therapy”; U.S. Pat. No. 5,394,452 Verification system for radiation therapy”; and U.S. Pat. No. 5,317,616 “Method and apparatus for radiation therapy”; all assigned to the assignee of the present invention and hereby incorporated by reference.
While Tomotherapy provides for a high degree of accuracy and precision in the placement of dose, standard radiation therapy gantries, moveable in multiple dimensions, may be preferred for certain treatments, for example, treatments of breast tumors, where out-of-plane gantry locations may limit exposure of the patient's chest cavity. In this case, precision of dose placement is traded off against the ability to limit dose to other body structures.
The increased accuracy of current Tomotherapy systems is limited by physical constraints related to creating narrower occluding leaves, such as define the width of the modulated rays within each radiation beam, accurately locating the tumor, accommodating a range of patient body sizes, and controlling for patient motion.